The present invention relates to a valve with a venting mechanism. It finds particular application in conjunction with a tractor protection valve for heavy vehicles and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other applications.
Different types of heavy vehicles include straight vehicles (e.g., vehicles having a cargo body and a tractor mounted on the same chassis) and articulated vehicles (e.g., vehicles having a cargo body and a tractor mounted on different chassis). Articulated heavy vehicles typically include a tractor portion and a trailer portion. Many common vehicle systems on the tractor and the trailer portions require fluid (e.g., compressed air or pneumatic fluid) to operate. Connecting lines between the tractor and the trailer communicate the fluid between the tractor and trailer portions for operating the various vehicle systems. For example, a supply connecting line transmits pressurized fluid (e.g., compressed air) from the tractor to the trailer for use as supply pressure by a trailer brake system; a control connecting line transmits pressurized fluid (e.g., compressed air) from the tractor to a control volume on the trailer for use as control pressure by service brakes on the trailer. In this design, a pressure signal is supplied via the control connecting line to apply the trailer service brakes when a vehicle operator depresses a brake pedal on the tractor.
The connecting lines are typically connected to a valve (e.g., a tractor protection valve), which is mounted on the tractor, through which the fluid is communicated between the tractor and trailer portions of the vehicle. In the event of a leak in the vehicle air system or one of the connecting lines, or if one of the connecting lines become separated from either the trailer or the tractor protection valve, the fluid may leak at a rapid rate (e.g., compressed air intended for the trailer brake system may, instead, be rapidly vented to atmosphere). In this case, the tractor protection valve will operate to reduce or prevent the unintended leakage of the fluid. For example, if the trailer becomes separated from the tractor, the tractor protection valve prevents or reduces the loss of pressure on the tractor so that the tractor (and the tractor braking system) can continue to operate safely. Trailers typically include parking brakes (spring brakes) that are automatically applied if the supply pressure to the trailer is lost.
If the pressure of the trailer supply air, which is provided from the tractor protection valve to the trailer via the supply connecting line, drops below a predetermined threshold (e.g., if a leak develops in the air supply system, or if the supply connecting line is disconnected from either the tractor protection valve or the trailer), a valve on the tractor protection valve closes to prevent pressurized fluid being supplied to the control volume on the trailer. Closing the valve on the tractor protection valve to prevent pressurized fluid from being supplied to the control volume on the trailer may cause pressurized air to become trapped in the control volume, which may cause the trailer service brakes to be applied. As discussed above, once the trailer supply air pressure is below the predetermined threshold, the trailer parking brakes may be applied. Simultaneous application of the service brakes and the parking brakes on, for example, the trailer is commonly referred to as service brake and spring brake compounding. Service brake and spring brake compounding on, for example, the trailer is undesirable. Therefore, in order to prevent service and spring brake compounding on the trailer, air trapped in the control volume is typically vented to atmosphere when the parking brakes are applied.
It is desired to reduce the complexity and manufacturing costs associated with current tractor protection valve designs while ensuring the service brake control volume is vented when trailer supply pressure to the tractor protection valve drops below the predetermined threshold.
The present invention provides a new and improved apparatus and method which addresses the above-referenced problems.